Central Indian Ocean Basin micrometeorite collections: Type, flux, etching and its implication to ocean biogeochemistry

Abstract

Extraterrestrial phenomena have influenced Earth’s processes throughout geological history. Evaluating the impact of extraterrestrial material on the environment is crucial for understanding the evolution of Earth and life. This study incorporates the investigation of micrometeorites (MMs), abundant cosmic materials on Earth, to understand their influence on the chemical composition and biogeochemistry of the ocean. Comprehensive etching and flux analyses reveal that ∼95% of cosmic spherules (CSs) entering seawater are etched or wholly dissolved, supplying nutrients to phytoplankton. Barred spherules show the highest degree of etching (∼19%), followed by porphyritic (∼17%), glass (∼15%), cryptocrystalline (∼12%), scoriaceous (∼10%), G-type (∼9%), and I-type (∼6%). Annually, ∼3080 tonnes (t) of olivine from MMs dissolve into seawater, contributing ∼495 t of Mg²⁺, ∼1110 t of Fe²⁺, and ∼1928 t of silicic acid. This signifies that over the Indian Ocean’s ∼40 Myr history, ∼23 Gt of olivine from CSs has dissolved, providing nutrients to seawater and sequestering ∼7 Gt of CO₂. The world ocean during this time has sequestered ∼35 Gt of CO₂, with fluctuations influenced by extraterrestrial activity. For instance, the Veritas event, lasting ∼1.5 Myr, sequestered ∼6 Gt of CO₂ from the atmosphere. A robust flux calculation based on ∼2 t of deep-sea sediments from 3610 MMs provides a more accurate estimate of the time-averaged flux of ∼229 t yr⁻¹. These comprehensive analyses reveal MM’s original characteristics, post-deposition processes, geological record and their overall impact on Earth’s marine environments, thereby contributing to our knowledge of the interconnection between terrestrial and extraterrestrial processes.